Revision Control System (RCS) – stores the latest version and backward deltas for fastest access to the trunk tip[1][2] compared to SCCS and an improved user interface,[3] at the cost of slow branch tip access and missing support for included/excluded deltas.

Source Code Control System (SCCS) – part of UNIX; based on interleaved deltas, can construct versions as arbitrary sets of revisions. Extracting an arbitrary version takes essentially the same time and is thus more useful in environments that rely heavily on branching and merging with multiple "current" and identical versions.